In recent years, in the trend of reduction in power consumption such as prevention of global warming and energy saving laws, production facilities are also required to reduce power consumption. Compressed air that is generated by compressing air in the atmosphere is widely used as a power source for driving a pneumatic tool, an air press, an air brake, a spray gun, and the like, because it gives users ready access. Hereafter, devices driven by compressed air are collectively referred to as terminal devices. The compressed air is compressed by an air compressor and supplied to the terminal device via a piping network provided in production facilities. It is said that power consumption of the air compressor accounts for 20 to 30% of the power consumption of an entire production facility, and it is necessary to reduce the power consumption of the air compressor in order to save energy at the production facility.
In order to reduce the power consumption of the air compressor, it is desirable to reduce discharge pressure of the air compressor as much as possible. On the other hand, in order to stably operate the terminal device, it is necessary to set the pressure of compressed air to be supplied to the terminal device to a desired pressure or more. A pressure loss of the piping network which supplies the compressed air compressed by the air compressor to the terminal device varies with the changes in the discharge air flow rate of the air compressor and the consumption air flow rate of the terminal device. Therefore, in general, the discharge pressure of the air compressor is set in anticipation of the maximum pressure loss of the piping network so that the supply pressure to the terminal device is equal to or higher than the desired pressure. As a result, compressed air having a pressure equal to or higher than a desired pressure can be supplied to the terminal device. However, in a case where the consumption air flow rate is small, since the discharge pressure of the air compressor is set high even though the pressure loss of the piping network is small, the air compressor is driven at a pressure which is more than necessary, and excess power is consumed.
In order to cope with this problem, Patent Literature 1 discloses an air compressor operation control device for supplying compressed air having a pressure equal to or higher than a desired pressure to a terminal device while reducing power consumption of the air compressor by variably controlling a rotational speed of an electric motor that drives an air compressor so that supply pressure to the terminal device and a discharge pressure of the air compressor are measured, and the supply pressure to the terminal device becomes equal to or higher than a desired pressure according to the consumption air flow rate at the terminal device.
In addition, Patent Literature 2 discloses a technique for determining operating conditions of an air compressor in which a record of a past operating condition of the air compressor is stored using a learning function, and the record of the past operating condition is referred to the current measurement values of the air compressor power consumption, an air compressor discharge pressure, and the supply pressure to the terminal device, whereby the technique can supply compressed air having a pressure equal to or higher than a desired pressure to the terminal device while reducing power consumption of the air compressor.